1. Technical Field
The present invention relates to a wiring member used in a liquid ejection head such as an inkjet recording head, and to a liquid ejection head having the same. More particularly, the invention relates to a liquid ejection head wiring member having wiring terminal rows formed by arranging wiring terminals corresponding to the pressure generating elements of a liquid ejection head arrayed in rows, and to a liquid ejection head having the wiring member.
2. Related Art
One type of liquid ejection head that discharges fluid droplets from a nozzle by varying the pressure of the fluid inside a pressure chamber discharges fluid droplets by deforming a piezoelectric element (a type of pressure generating element) connected to a diaphragm. This type of liquid ejection head discharges droplets from the nozzles using the change in pressure produced by applying a drive voltage (drive pulse) to drive the piezoelectric element to change the volume of the pressure chamber, thereby varying the pressure of the fluid stored in the pressure chamber.
The piezoelectric element is electrically connected to a COF (Chip On Film), TCP (Tape Carrier Package) or other type of flexible printed circuit having a semiconductor chip for driving the piezoelectric element, and drive voltage is supplied thereto through the flexible printed circuit. See, for example, JP-A-2005-254616. The piezoelectric element includes a bottom electrode layer, a piezoelectric layer, and a top electrode layer. Generally, one electrode (for example, the bottom electrode layer) is used as a common element electrode connected in common to a plurality of piezoelectric elements, and the other set of electrodes (for example, the top electrode layer) are used as individual element electrodes connected to the individual piezoelectric elements. The piezoelectric layer disposed between the common element electrode and the individual element electrodes is the active piezoelectric portion in which piezoelectric strain is produced by applying a drive voltage to the electrodes.
FIG. 7 schematically describes the layout of the element electrodes of the piezoelectric elements and the element electrode wiring units (lead electrode units) extending from the element electrodes in the actuator unit 69 (refer to FIG. 8) of a recording head according to the related art. Note that the dark hatching in the figure indicates the individual element electrodes and the individual element electrode wiring units electrically connected thereto, and the light hatching indicates the common element electrode and the common element electrode wiring unit electrically connected thereto. Note also that the nozzles (piezoelectric elements) are oriented vertically as seen in the figure. Each pressure chamber and each piezoelectric element are coupled to each of the nozzles, and only two rows of nozzles are shown in the figure.
In the configuration shown in the drawing, common element electrode 70 that is connected in common with the piezoelectric elements is continuously formed in the nozzle row direction on an elastic film (not shown) defining part of each pressure chamber, and a piezoelectric layer (not shown) and an individual element electrode 71 are sequentially laminated thereon in a pattern corresponding to each of the piezoelectric elements. An individual element electrode terminal 72 (a type of individual element electrode wiring unit) electrically connected to an individual element electrode 71 is formed between the adjacent nozzle rows for each of the individual element electrodes 71. The individual element electrode terminals 72a corresponding to one nozzle row (the left side in the drawing) and the individual element electrode terminals 72b corresponding to the other nozzle row (the right side in the drawing) are arranged in alternating rows in the nozzle row direction. The individual element electrode terminals 72 are the parts that are electrically connected to the individual electrode wiring terminals 77 on one end of a flexible printed circuit 68 (see FIG. 8).
Further, a common element electrode unit 73 (a type of common element electrode wiring unit) is formed surrounding the area where the common element electrode 70, the individual element electrode 71, and the individual element electrode terminal 72 are formed.
The common element electrode unit 73 is a frame including a common vertical electrode unit 73a and a common transverse electrode unit 73b. The common vertical electrode unit 73a extends in the nozzle row direction on the outside of each nozzle row (the opposite side as the side on which the individual element terminals are formed). The common transverse electrode unit 73b extends in a direction perpendicular to the nozzle row direction on both ends of the nozzle row direction. The common element electrode unit 73 is electrically connected to the common element electrodes 70 via each branch electrode unit 74.
A common element electrode terminal 75 that is connected to the common electrode wiring terminal 78 of the flexible printed circuit is rendered in portions of the common element electrode unit 73 at positions on opposite sides of the individual element electrode terminals 72 in the nozzle row direction as indicated by the dotted circles in the figure.
As shown in FIG. 8, the flexible printed circuit 68 has a configuration in which a control chip 76 that controls applying the drive voltage to the piezoelectric elements, and a wiring pattern including individual electrode lines and common electrode lines (not shown in the figure), are disposed to the surface of a polyimide or other type of base film, and the control chip 76 and the wiring pattern are then covered by a resist without covering the wiring terminals (individual electrode wiring terminals 77 and common electrode wiring terminals 78).
Further, multiple individual electrode wiring terminals 77 corresponding to the individual element electrode terminals 72 of the actuator unit are formed on one end of the flexible printed circuit. A common electrode wiring terminal 78 corresponding to the common element electrode terminal 75 of the actuator unit is also formed at this end of the FPC 68 at the outside end of the row of individual electrode wiring terminals 77.
Generally, the wiring terminals, the wiring pattern, and the control chip 76 are rendered on only one side of the flexible printed circuit 68. In addition, when wired to the actuator unit 69, this end of the flexible printed circuit is bent between the wiring terminals and the wiring pattern at a substantially right angle to the opposite side as the side on which the wiring pattern is formed. Each of the wiring terminals 77 and 78 is solder plated, and the wiring terminals 77 and 78 are soldered and thereby electrically connected to the corresponding element terminals 71 and 75 of the actuator unit, and the flexible printed circuit 68 is connected to the actuator unit 69.
However, with the recording head according to related art as described above, the common electrode wiring, the individual electrode wiring, the wiring terminals, and the drive control IC are provided on one side of the flexible printed circuit, and the area occupied by the common electrode wiring is significantly smaller than the area occupied by the drive control IC and individual electrode wiring due to installation space limitations. If the wiring space used for the common electrodes, including the common element electrode wiring unit of the actuator unit, is narrow, the resistance of the electrode may cause a voltage drop in the electrode surface, causing the drive voltage applied to the piezoelectric element to fluctuate and the amount or velocity of the ink discharged from the nozzle to vary. The likelihood of this problem occurring increases as the number of simultaneously discharging nozzles increases.
To solve this problem, the recording head according to the related art requires a larger area for the common element electrode wiring unit of the actuator unit, and prevents reducing the size of the recording head accordingly.